Coleman Mach Q 15KBTU AC Lo Circuit Failure

[haznavy]

Good morning,

2022 Solitude 378MBS 3 AC rig with fault in aft-most AC Lo circuit. Fault presents as follows when operating from thermostat:

1. Fan LO - BAD
2. Fan HI - GOOD
3. Cool HI - GOOD
4. Cool LO - BAD
5. Cool LO Auto - BAD
6. Cool HI Auto - GOOD

1). Thermostat wiring and connection points look good to me; 2). Replaced blue ground wire on the roof to control box which snapped when conducting PMS; 3). On roof wiring ohm out from points A to B; 4). Nothing visually amiss in the control box.

Unable to find Mach Q wiring diagram to find common location for Hi/Lo circuitry.

Any assistance would be most appreciated.

[howson]

Good morning,

2022 Solitude 378MBS 3 AC rig with fault in aft-most AC Lo circuit. Fault presents as follows when operating from thermostat:

1. Fan LO - BAD
2. Fan HI - GOOD
3. Cool HI - GOOD
4. Cool LO - BAD
5. Cool LO Auto - BAD
6. Cool HI Auto - GOOD

1). Thermostat wiring and connection points look good to me; 2). Replaced blue ground wire on the roof to control box which snapped when conducting PMS; 3). On roof wiring ohm out from points A to B; 4). Nothing visually amiss in the control box.

Unable to find Mach Q wiring diagram to find common location for Hi/Lo circuitry.

Any assistance would be most appreciated.

Typically the gray wire on the thermostat is the LO circuit.


At the Control Box the Low Fan circuit should also be the GL input.


An easy test is to swap the wires (the GH and GL wires on the control box) to see if the problem follows. If (after swapping the HIGH and LO fan circuit inputs on the control box) the HIGH fan fails then the fault is either in the thermostat or the wiring to the control box. If the LO still doesn't work, the problem is in the control box or in the a/c unit itself.

To be safe, remove 12vDC power (thermostat should go blank) and 120vAC to the control box (turn off shore power or flip applicable circuit breaker) when swapping wires. Also--take good pictures BEFORE moving anything to ensure it can be put back original. (Ask me how I know...)

Pls report back with the results.

Howard

[haznavy]

Here's what we found when troubleshooting with an Airxcel tech:



Is this a ducted application running off a wall tstat? If so, (YES) and it looks like the low fan operator is failed on all the issues, what is the voltage leaving the wall thermostat between the B and GL terminals (blue and gray if the tstat has our wires attached to it).

A: There is 13vdc between red and blue only when lo cool or lo cool auto are selected at the tstat.

*******Tod,

Just so we are clear, in the image below you have 13VDC between these two terminals? (YES)



In the image below, you do not have any DC voltage between these two terminals when calling for low fan / low cool? (10vdc)




If this information is accurate, you will need a new thermostat. What is the serial number of your AC unit, the date of purchase?

The model/serial number of the AC unit can be found by removing the shroud and looking at the 4x6 inch data tag on the side of the AC unit. Or this can be found by removing the ceiling assembly filter inside of the coach and shining a flashlight into the return air of the AC unit, you should see a small sticker with the model and serial number.


Casey Caide

Technical Assistance Coordinator

RV Products, a division of Airxcel, Inc.

3050 N. St. Francis

Wichita, Kansas 67219

Office: 574-247-9235

www.Airxcel.com